As much as 30% of the geriatric population complains of poor sleep quality, a complaint that is validated by objective findings showing reduced slow wave sleep (SWS) and increased time and frequency of awakenings during sleep in elderly compared to younger individuals. The physiological consequences of age impaired sleep are poorly understood, but may include impaired anabolic hormone status and damped circadian rhythms. Poor sleep may also account for the disproportionate prescription of sedative hypnotics in the elderly population. Hypnotic medication offers only short term efficacy and in the long term may itself disrupt sleep. Hypnotic use may also lead to exacerbation of sleep apnea and daytime carryover effects such as sedation, falls, cognitive impairment and anterograde amnesia and has been associated with increased morbidity and mortality. Non- pharmacological interventions to improve sleep quality in the elderly population are obviously needed. One such treatment might be regular exercise leading to increased aerobic fitness. Physical fitness in older individuals has been associated with decreased incidence of coronary heart disease, increased strength and vigor, improvements in cognitive functioning and attenuates and perhaps reverses age-related declines in physiological and psychological functioning which may be at least partially the result of inactivity. Daytime exercise has been shown to increase nighttime SWS in young physically fit individuals. Young unfit individuals show enhancement of SWS following a period of physical training. Surprisingly, the effects of improved aerobic fitness on sleep have never been examined in the elderly. The proposed study will examine the effects of improved aerobic fitness resulting from a six month (3 day/week) aerobic training program on objective and subjective sleep quality and on physiological correlates of sleep (circadian temperature rhythm, nighttime growth hormone secretion (and basal daytime somatomedin-c levels) and basal nighttime plasma norepinephrine levels) of 30 men, 60 to 80 years of age, compared to a matched control group of 30 men who participate in a six month (3 day/week) program of relaxation/stretching. Improved aerobic fitness is hypothesized to be associated with improved objective and subjective sleep quality, increased circadian temperature amplitude, increased growth hormone and somatomedin-c levels and decreased nighttime norepinephrine levels.